Many modern electronic devices contain digital memory (e.g., a dynamic random access memory, DRAM). Each memory may be used to store information for a digital device. Users of such electronic devices typically desire large amounts of memory in a small package. Where the electronic devices are portable (e.g., battery powered), users may also desire electronic devices which do not consume as much power and therefore have a longer battery life. Thus, manufacturers of electronic devices typically desire small, high density memories with low power consumption.
To meet the demand for small, high density memories, memory manufacturers typically create memory chips with the smallest available features (e.g., transistors and control lines) and with densely packed memory cells. However, as the size of features in a memory chip shrinks and as the memory density of a memory chip increases, errors in the manufacturing process may cause more defective memories at a high cost to the manufacturer.
An example of a possible defect in a memory device is a short (e.g., an unintended electrical connection) between a defective wordline and a bitline of a memory device. Wordlines and bitlines are lines in a memory device which are used to access a memory cell (e.g., at the junction of the wordline and bitline) in the memory device. Where a wordline and bitline are shorted, the memory cell located at the junction of the wordline and bitline may, in some cases, not be accessible, thereby resulting in a defective memory cell and defective memory device.
To reduce the number of defective memory devices resulting from defective wordlines and/or bitlines, many manufacturers create memory devices with redundant wordlines and/or bitlines. Where, for example, the manufacturer detects a defective wordline, the memory device may use a redundant wordline instead of the defective wordline. When a memory device uses a redundant wordline instead of a defective wordline, the defective wordline may be referred to as a repaired wordline.
While repairing a defective wordline may prevent a memory device from losing data, the defective wordline may still remain shorted to a bitline. In some cases, where a defective wordline is shorted to a bitline, current may flow between the defective wordline and the bitline, thereby increasing the power consumption of the memory device. Therefore, there is a need to not only repair the defective wordline, but also to reduce the power consumption of the memory device due to the defective wordline.
Further, it is generally desirable to perform repair operations quickly in order to reduce the amount of time used for testing a memory device, thereby reducing the overall cost of the memory device. Furthermore, to maintain a low overall cost of the memory device, there may be a desire to locate defective wordlines without increasing the complexity of the test method and/or memory device.
Accordingly, what is needed is an improved method and apparatus for locating and repairing defective wordlines.